1. Field of the Invention
This invention relates to new liquid-crystalline substances which exhibit a liquid-crystalline phase in a broad temperature range, and compositions containing the same.
2. Description of the Prior Art
Display elements using liquid crystals have come to be widely used for watches, desk calculators, etc. Such liquid-crystalline display elements utilize optical anisotropy and dielectric anisotropy of liquid-crystalline substances, and their liquid-crystalline phases include nematic liquid-crystalline phase, smectic liquid-crystalline phase and cholesteric liquid-crystalline phase, and those utilizing nematic liquid crystals among them have been most broadly employed for practical uses. Further, liquid-crystalline display elements include those of TN type (twisted nematic type), DS type (dynamic scattering type), guest-host type, DAP type, etc. and properties required for liquid-crystalline substances used therefor are varied. At any rate, however, as liquid-crystalline substances used for these display elements, those which exhibit a liquid-crystalline phase within as broad a range as possible in the natural world have been desired. However, no single compounds satisfying such a requirement have been found to date, and it is the present status that liquid-crystalline compositions which are practically usable for the present have been obtained by mixing together several kinds of liquid-crystalline compounds or non-liquid-crystalline compounds. Further, these substances, of course, must be stable to moisture, heat, air, etc., and moreover, it has been desired for the substances that the threshold voltage and saturation voltage required for driving the display elements be as low as possible and the viscosity be as low as possible for making the response speed higher. Further, for broadening the liquid-crystalline temperature range toward the higher temperatures, it is necessary to employ a high melting liquid-crystalline substance as a component, but such a high melting liquid-crystalline substance generally has a high viscosity and accordingly a liquid-crystalline composition containing it also has a high viscosity; hence there has been a tendency that the response speed of liquid-crystalline display elements as usable up to e.g. 80.degree. C., particularly that at lower temperatures, becomes notably slow.
The present inventors previously invented 1-alkyl-4-[trans-4-(trans-4-alkylcyclohexyl)cyclohexyl]benzenes expressed by the general formula ##STR3## as one of liquid-crystalline compounds improving the low temperature characteristic, and filed a patent application claiming the same (Japanese patent application laid-open No.Sho 57-165,328/1982).
However, recent technical advance of liquid-crystalline display elements has been so remarkable that display elements being actuated at a temperature ranging from a further lower temperature to a higher temperature have been required.
The object of the present invention is to provide a liquid-crystalline compound corresponding to such a requirement, that is, exhibiting a liquid-crystalline phase within a broader temprature range and also having a high transparent point and yet a low viscosity.